This invention relates to a rotation transmission device mounted in the powertrain of a vehicle to selectively transmit torque between input and output members.
JP patent publication 2003-191769A discloses a rotation transmission device mounted on a four-wheel drive vehicle based on the front-engine, rear-wheel drive layout to selectively transmit torque to the front wheels as auxiliary drive wheels.
The rotation transmission device disclosed in this publication includes an outer ring coupled to a propeller shaft of the vehicle, and an inner ring coupled to a pinion shaft of a differential of the vehicle. A two-way clutch is mounted between the inner and outer rings. An electromagnetic clutch is provided in juxtaposition with the two-way clutch to selectively engage and disengage the two-way clutch. When the two-way clutch engages, the inner and outer rings are rotationally coupled together, so that torque is transmitted from the outer ring to the inner ring.
The two-way clutch comprises a cylindrical surface formed on the inner periphery of the outer ring, a plurality of cam faces formed on the outer periphery of the inner ring so as to radially oppose the cylindrical surface of the outer ring, rollers each received in one of wedge-shaped spaces defined between the cylindrical surface and the cam faces and having narrow circumferential ends, and a retainer retaining the rollers in position. When the retainer rotates relative to the inner ring, the rollers are moved by the retainer into engagement with the cylindrical surface and the cam faces. A switch spring is mounted between the inner ring and the retainer to bias the retainer toward its neutral position where the rollers are not in engagement with the cylindrical surface and the cam faces.
The electromagnetic clutch comprises an armature rotationally fixed but axially movable relative to the retainer, a rotor rotationally fixed to the outer ring and axially facing the retainer with the armature disposed therebetween, and an electromagnet axially facing the armature with the rotor disposed therebetween. By energizing the electromagnetic coil of the electromagnet, the armature is magnetically attracted toward the electromagnet until pressed against the rotor. Thus, the retainer, which is rotationally fixed to the armature, rotates together with the outer ring and thus rotates relative to the inner ring. The rollers are thus moved by the retainer into engagement with the cylindrical surface and the cam faces.
The electromagnet is mounted to a stationary member or housing. But depending upon machining accuracy of the parts forming the electromagnet, the electromagnet may be supported unstably on the housing such that the electromagnet is axially movable. This may make it difficult to rotate the retainer relative to the inner ring against the force of the switch spring until the rollers fully engage the cylindrical surface and the cam faces, thus destabilizing the operation of the two-way clutch.
Also, if the electromagnet is unstably mounted, it tends to vibrate when the vehicle vibrates, thus producing noise.
In order to stably mount the electromagnet, JP patent publication 2003-191769A proposes to secure a flange to a core supporting the electromagnetic coil of the electromagnet. The flange is received in a recess formed in the stationary member. A snap ring is engaged in a groove formed in the inner periphery of the recess. An elastic member is disposed between the snap ring and the flange to press the flange against the end wall of the recess.
In this arrangement, because the elastic member is disposed between the flange and the snap ring, in order to axially position the electromagnet by pressing the electromagnet against the end wall of the recess, the elastic member has to have a spring force greater than the sum of the product F1 of the axial vibration G and the weight W of the electromagnet and the load F2 applied to the elastic member when the electromagnet is pulled toward the rotor under the magnetic attraction produced when the electromagnet is energized. Thus, the elastic member has to have a sufficiently large spring force.
Because the elastic member has a large spring force, it is necessary to compress the elastic member with a large force to mount the snap ring in the groove. It is thus troublesome and time-consuming to mount the snap ring. Also, as the elastic member, one having a diameter larger than the outer diameter of the core has to be used. Such an elastic member is naturally costly.
Such conventional rotation transmission devices comprise a large number of parts because they need the flange secured to the core, the snap ring and the elastic member disposed between the flange and the snap ring in order to axially position the electromagnet. Further, since the flange is a separate member from the core and has to be secured to the core by welding or caulking a rivet, the cost for fixing the flange to the core is high.
A first object of the present invention is to provide a rotation transmission device in which the electromagnet of the electromagnetic clutch can be axially positioned using an elastic member that is smaller in spring force and thus less costly than those used in conventional rotation transmission devices, whereby the snap ring can be mounted more easily.
A second object of the invention is to provide a rotation transmission device in which the electromagnet of the electromagnetic clutch can be axially positioned with a simpler and less costly positioning structure.